The heat added during the transformation from solid to liquid state without a change in temperature is called latent heat of fusion.

Here's why:

* Latent heat refers to the energy absorbed or released during a phase change without a change in temperature.

* Fusion is the process of changing from a solid to a liquid.

So, the heat added during this process is the latent heat of fusion. This energy is used to break the bonds between the molecules in the solid state, allowing them to move more freely and become a liquid.